1. Field of the Invention
The present invention relates to a recording apparatus for recording a character, an image, and/or the like by discharging ink onto a recording medium such as a recording sheet, and more particularly, it relates to a recording apparatus including guide members for guiding a recording medium to a discharge roller.
2. Description of the Related Art
Commercially available recording apparatuses performing a recording operation on a recording medium such as a recording sheet or a sheet for an overhead projector (OHP) have a variety of recording heads mounted thereon, including those of a wire dot type, a thermal type, a thermal transfer type, and an inkjet type. In particular, a recording head of an inkjet type is known as a recording component whose operational cost is inexpensive and which operates with a relatively low noise level since it directly discharges ink onto a recording medium.
FIG. 20 is a perspective view of a known inkjet printer (hereinafter, referred to simply as a printer). For the sake of easy understanding, a part of an outer casing of the printer is omitted. Also, FIG. 21 is a sectional view of the known printer, while a part thereof unnecessary for explanation is omitted.
As shown in FIGS. 20 and 21, the known printer includes a recording unit 100, including a carriage 101 having a recording head mounted thereon, for recording an image and/or the like on a recording medium; an automatic feed unit 102 for feeding a recording medium; a transport unit 103 for transporting the recording medium to the recording unit 100 in the arrow T direction indicated in FIGS. 20 and 21; and a discharge unit 105 for discharging the recording medium having a recording operation performed thereon by the recording unit 100.
When the printer receives a recording signal, a plurality of recording media stacked in the automatic feed unit 102 are individually separated by separation means (not shown) and are transported sheet by sheet.
At the transport unit 103, a recording medium is transported by a transport roller 106 and a transport pinch roller 107. When the transport unit 103 transports a recording medium by a length corresponding to a recording width of the recording head, the printer causes the carriage 101 to sweep and sequentially performs a recording operation on the recording surface of the recording medium by driving and controlling the recording head in accordance with a recording signal. The recording unit has a platen for guiding the other side of the recording surface of the recording medium. After completion of the recording operation, the recording medium is transported to the discharge unit 105.
As shown in FIG. 21, the transport unit 103 includes the transport roller 106 and the transport pinch roller 107. The transport roller 106 has a coating material containing ceramic particles applied on the surface thereof and transports a recording medium with a friction generated between the recording medium and the transport roller 106 by pressing the recording medium with the transport pinch roller 107. The transport roller 106 has a platen 112 disposed downstream therefrom for guiding a part of the recording medium facing the recording head mounted on the carriage 101.
The platen 112 has a set of a first discharge roller 108 and a first discharge pinch roller 109 and a set of a second discharge roller 110 and a second discharge pinch roller 111, all disposed in the downstream region thereof along the arrow T direction serving as a transport direction of the recording medium. The transport surface of each of the first and second discharge rollers 108 and 110 is composed of a high-friction material such as rubber having a relatively large coefficient of friction. The first and second discharge pinch rollers 109 and 111 are disposed so as to be pressed towards the first and second discharge rollers 108 and 110, respectively.
FIG. 22 is a partial sectional view of the printer, illustrating a state in which a recording medium 113 is traveling in the vicinity of the first discharge roller 108. A relative position between the platen 112 and the first discharge roller 108 in the height or vertical direction is set such that the top part of the peripheral surface of the first discharge roller 108 lies slightly higher than the recording-medium guiding-surface of the platen 112. When the platen 112 lies higher than the top part of the first discharge roller 108, a pressing force of the first discharge pinch roller 109 decreases due to elasticity of a recording medium, thereby deteriorating a discharge performance. Since the relative position between the platen 112 and the first discharge roller 108 in the height direction is set such that the top part of the peripheral surface of the first discharge roller 108 lies slightly higher than the recording-medium guiding-surface of the platen 112, the recording medium 113 guided by the platen 112 abuts first against the first discharge roller 108.
The transport speed of the first discharge roller 108 is arranged so as to rotate at nearly the same speed as that of the transport roller 106. When the transport speed of the first discharge roller 108 is lower than that of the transport roller 106, a recording sheet is sometimes deformed at the recording unit. As a countermeasure against this problem, taking tolerances and other characteristics of the discharge roller and the transport roller into account, in general, the former is often designed so as to rotate slightly higher than the latter. Here, the circumferential speed of the peripheral surface of the first discharge roller 108 is defined as VA. As shown in FIG. 22, when the leading edge of the recording medium 113 abuts against the first discharge roller 108, the speed of the recording medium 113 in the horizontal transport direction becomes VB, thereby resulting in being slightly lower than the original design speed VA.
Hence, during a transitional period of the leading edge of the recording medium 113 being introduced to the first discharge roller 108, the traveling speed of the recording medium 113 is sometimes slightly altered.
Since the recording head of an inkjet type is used performing a recording operation by ejecting ink droplets onto the recording surface of a recording medium, the recording operation is performed in a non-contact state between the recording medium and the recording head. A decrease in speed of an ink droplet due to an air drag and the like during ejection toward the recording medium sometimes causes the ink droplet to fly in a different direction from the originally designed one. In order to solve this problem, it is preferable that the recording medium and the recording head lie close to each other, and hence the distance therebetween is generally set in the range from 0.5 mm to 1.5 mm.
Meanwhile, a variety of recording media including from a sheet of relatively thin normal paper to a relatively thick envelope are used. When a relatively thick recording medium is used, it is expected that the recording head and the recording medium come into contact with each other. In order to avoid such a contact, many printers have a structure in which an operator can adjust the distance between the platen for supporting the recording medium and the recording head in accordance with the thickness of a recording medium. A carriage moving method and a platen moving method are known methods for adjusting the distance between the platen and the recording head.
As shown in FIG. 22, when the platen moving method is employed, since the abutment position between the leading edge of the recording medium 113 and the first discharge roller 108 lies below the top of the peripheral surface of the first discharge roller 108, the speed VB of the recording medium becomes lower than VA, thereby leading to an increase in so-called printing irregularity.